A safety lock is placed on the edge of the exit tube, inside of the oil separator, and it´s purpose is to prevent the leakage of separated light oils in a natural recipient. It is made of a float which is moving along the separation line between water and light fluids. When the level of light fluids is increased, the float is falling and getting near the pipe opening. In the moment when the level of light fluid is increased so much that it threats to get out into the recipient, the float gets into the pipe opening and prevents its leakage from the separator.